Pneumatic tire including steeply slanted grooves, rib having sipes and blocks having sipes

ABSTRACT

A tire tread for a pneumatic tire has a center rib and a series of steeply slanted grooves in each side region of the tread, the circumferentially adjacent grooves form blocks extending through the tread side regions. The center rib has a serrated configuration along each lateral side and a supporting chamfer extending from each serration point. Adjacent to each rib chamfer is a chamfer extending from the axially innermost point of the rib at the junction of two adjacent steeply slanted grooves. The rib is provided with high density siping. The tread blocks are siped wherein the siping density decreases from the tread center to the tread shoulders.

FIELD OF THE INVENTION

The present invention is directed to a tire tread with improvedperformance in snow and ice and in regular running conditions. The treadis provided with a central rib and a series of steeply slanted groovesadjacent the rib. The rib and the adjacent tread blocks are configuredto provide for improved all weather performance.

BACKGROUND OF THE INVENTION

In a conventional tire for typical use as on a passenger car or lighttruck, the tire tread is provided with a series of grooves, eithercircumferentially or laterally extending, or a combination of both, toform a plurality of blocks.

The goals of a tire during winter driving condition are to maintain goodcontact with the road, while providing for enhanced traction. However,since enhanced traction is best achieved by providing most biting edgesto the tread pattern, while road contact is achieved by providing moresurface area for tread contact, these goal are often conflicting.

SUMMARY OF THE INVENTION

The present invention is directed to a tire with improved winter drivingcondition.

Disclosed is a pneumatic tire comprising a tread and shoulders adjacentthe tread, the tread comprising a central region and a pair of opposingside regions. The tread has a circumferentially extending rib in thecentral region, and a plurality of steeply slanted grooves inclined atan angle relative to the circumferential direction of the tire in eachside region. The center rib has a plurality of sipes extending acrossthe full width of the rib, the sipes having a density of 2 to 8 sipesper inch (0.78–3.15 sipes per cm). Additionally, the steeply slantedgrooves in each side region initiate at the junction of the centralregion and the side regions and terminate in the shoulders, formingcircumferentially adjacent tread blocks. The blocks extend from thecentral region to the shoulders and have a plurality of sipes. Thespacing between adjacent sipes in the block increases toward the treadshoulders. The tread has a greater sipe density in the central region ofthe tire than in the side regions.

In one aspect of the invention, at the axially inner portion of theblock, the block has a sipe density of 1 to 5 sipes per inch (0.393–1.97sipes/cm). At the axially outer portion of the block, the block has asipe density of 0.5 to 3 sipes per inch (0.2 to 1.18 sipes/cm).

In one aspect of the tire, the lateral edges of the rib have a pluralityof laterally extending edges and circumferentially extending edges. Thelaterally extending edges on each side of the rib are circumferentiallyoffset from the laterally extending edges on the opposing side of theribs. Preferably, extending from the laterally oriented edges of therib, and along the lateral edge of the rib, are chamfers that decreasein width from the laterally oriented edge to the circumferentiallyadjacent laterally oriented edge.

In another aspect of the invention, the radial height of the rib chamfergradually decreases from the laterally oriented edge to thecircumferentially adjacent laterally oriented edge.

In another disclosed aspect of the invention, to increase the ribflexibility as the tread wears, the sipes of the tread rib extend intothe chamfers.

The sipes in the tread rib are formed of at least two inclined portions.When formed of two portions, the sipe portions ideally follow the sameinclination angle as the laterally oriented edges of the rib. In oneembodiment, the sipes are formed of three portions.

The sipes in the tread blocks are preferably oriented perpendicular tothe steeply slanted grooves. The tread block sipes may also be inclinedin the same direction as the most adjacent sipe portion of the treadrib.

In another aspect of the tire, the steeply slanted grooves have anon-constant width as the grooves extend from the central region to theshoulders, the grooves having a maximum width in the central 15% of eachside region of the tread. The grooves may have a maximum width of atleast 1.5 times the minimum groove width of the steeply slanted grooves.

In another aspect of the invention, the net-to-gross ratio of the tiredecreases from the tread edge toward the tread center, with a maximumnet-to-gross ratio at the equatorial plane of the tire.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a plan view of the tire;

FIGS. 2–5 are various embodiments of the rib chamfers;

FIGS. 5 a–5 b are cross sectional views taken of the chamfer of FIG. 5;

FIG. 6 is a portion of the rib and a chamfer illustrating anotherembodiment of the siping; and

FIG. 7 is another alternative of the tread.

DETAILED DESCRIPTION OF THE INVENTION

The following language is of the best presently contemplated mode ormodes of carrying out the invention. This description is made for thepurpose of illustrating the general principals of the invention andshould not be taken in a limiting sense. The scope of the invention isbest determined by reference to the appended claims.

FIG. 1 is a plan view of a tread for a tire in accordance with thepresent invention. The tread configuration is intended for use on apassenger vehicle, or a light truck. The illustrated tread has adirectional configuration, with the preferred direction for forwardmoving being that shown by the arrow D. The tread is divided into threeregions, a central region A, and two side regions B. The central regionis centered on the equatorial plane of the tire and has a width ofapproximately 15% to 30% of the tread width W, the tread width beingmeasured from one tread shoulder to the opposing tread shoulder.

When operating in winter driving conditions, the central region of thetire has the most impact on the performance of the tire. In the presenttire tread, the center of the tread is provided with a continuouslyextending rib 10. The rib 10 has sipes 12 extending across the fulllateral width of the rib 10. The rib 10 has a heavy sipe density, withinthe range of 2 to 8 sipes per inch (0.78 to 3.15 sipes/cm), with apreferred density of 3 to 7 sipes per inch (1.18 to 2.76 sipes/cm). Thepresence of the rib 10 provides good ground contact of the tire, whilethe heavy siping of the rib 10, and thus the central region of the tiretread, provides for increased traction as the multiple sipes 12 flexopen providing tread edges when the tread contacts the ground.

The rib sipes 12 have a non-linear configuration of at least twoinclined portions. The sipes 12 in FIG. 1 are formed of two inclinedportions 14, 16. The inclined portions 14, 16 are placed atsubstantially similar, but oppositely inclined angles to form an inverseV configuration, wherein the apex of the V is located at approximatelythe equatorial plane EP of the tire. The spacing betweencircumferentially adjacent sipes 12 is constant, but may be varied topermit pitching of the tire for optimization of the noisecharacteristics of the tire.

The sides 18, 20 of the rib 10, when viewed from above, has an extended,serrated configuration at the surface of the rib 10 that contacts theground when the tread is new and not-worn. Each serration 22 is formedfrom a laterally oriented edge 24 and an inclined circumferentiallyextending edge 26; the junction of the two edges forming a serrationpoint. The serrations 22 on each side 18, 20 of the rib 10 are laterallyoffset from each other. The laterally oriented edge 24 has a highinclination angle relative to the equatorial plane EP, while thecircumferentially extending edge 26 has a low inclination angle relativeto the equatorial plane EP.

Extending from the laterally oriented edge 24 along each side 18, 20 ofthe rib 10 is a chamfer 28. The chamfer 28 extends in a circumferentialdirection from the laterally oriented edge 24 of the serration 22 to thenext circumferentially adjacent serration 22, along the side 18, 20 ofthe rib 10.

Due to the chamfer 28, at the tread depth the rib 10 has an almoststraight configuration. The chamfers 28 have a greatest width where thechamfer 28 initiates at the laterally oriented edge 24 of the serration22. The width of the chamfer 28 narrows as the axially outermost edge 30of the chamfer 28 is substantially parallel to the equatorial plane EPof the tire while the sides 18, 20 of the rib 10 are inclined in thecircumferential direction. The provision of the chamfers 28 behind theheavily siped rib 10 provides support for the rib 10 as the sipes 12flex open, strengthening the rib 10 and maintaining good ground contactpressure for the rib 10.

FIG. 2 illustrates a side view of the chamfer 28. The chamfer 28 has amaximum width at the laterally oriented edge 24 of the serration 22, andgradually decreases in width as the chamfer 28 approaches the nextadjacent serration point 22. Concurrently, the height h of the chamfer28, as measured from the base of the tread depth, gradually decreases inthe circumferential direction, exposing the side wall 32 of the rib.

FIG. 3 illustrates a variation of the chamfer 28. The upper surface ofthe chamfer 28 is multi-planar. Where the chamfer 28 connects with thelaterally oriented edge 24, the surface is defined by a radius ofcurvature R1 located inward of the upper surface of the chamfer 28.Towards the base of the chamfer 28, the top surface is defined by aradius of curvature R2 located outward of the upper surface of thechamfer 28.

The chamfer 28 of FIG. 4 is a variation of that of FIG. 3 wherein a flatledge 34 is employed along the mid-length of the chamfer 28. The chamfer28 forms a tangency to a circle at several locations, as seen by R3 andR4.

In another embodiment of the chamfer 28, FIG. 5, the top surface of thechamfer 28 has a different multi-planar configuration. At the maximumlateral width, the top surface of the chamfer 28 slopes downward towardthe tread edge, see FIG. 5 a. As the chamfer width decreases, theaxially outer edge 30 of the chamfer 28, relative to the equatorialplane EP of the tire, gradually increases in height relative to the fulltread depth. Concurrently, the axially inner edge 36 of the chamfer 28decreases in height, see FIG. 5 b. Thus, as the width of the chamfer 28decreases, the height increases, causing the outer surface of thechamfer 28 to twist.

If maintaining tread flexibility as the tread is worn is desired, thesipes 12 in the center rib 10 may extend into the chamfers 28, see FIG.6. When the tread is unworn, the sipes 12 in the chamfers 28 do not openduring rotation as there is no contact with the road surface, and thechamfer 28 continues to provide support to the rib 10. After the treadbegins to wear, and the uppermost surface of the chamfer 28 slowlybecomes part of the ground contacting surface of the tread, theeffective rib width increases, and the siping of the chamfer 28 beginsto interact with the remaining tread. In effect, sipes 12 in the chamfer28 act as increased grooving of the tread as the tread depth decreasesdue to wear.

The laterally oriented edge 24 of each serration 22 is inclined at anangle of equal or less than 90°, but no less than 45° relative to theequatorial plane EP. In the tread of FIG. 1, the laterally oriented edge24 of each serration is inclined at approximately 45° relative to theequatorial plane EP. The laterally oriented edges 24 of each serration22 on each side 18, 20 of the rib 10 are inclined as offset mirrorimages of the each other. The circumferentially extending edge 26 isinclined at angle of approximately 0° to 30° relative to the equatorialplane EP of the tire. When the circumferentially extending edges 26 aresubstantially parallel to the EP, then the circumferentially adjacentlaterally oriented edges 24 are inclined in opposing directions; or elsethe rib 10 will “walk” across the tread. Because the chamfers 28 extendfrom the laterally oriented edges 24, the chamfers 28 on each side 18,20 of the rib 10 extend in the same direction.

Adjacent to the center rib 10, in each side region B of the tread, are aplurality of steeply slanted grooves 38. The grooves 38 in each sideregion B of the tread are circumferentially offset from the grooves 38in the opposing side region B. The grooves 38 initiate at the junctionof the center region A and the side regions B. At the junction, thegrooves 38 have a very low angle of inclination relative to the EP ofthe tire tread, and gradually increase in inclination. The majority ofeach groove 38 has a inclination angle α of 20° to 50° relative to thecircumferential direction of the tire, as measured by the centerline ofthe groove 38.

As the grooves 38 traverse the side regions B of the tread, the groovewidth varies. Close to the central rib 10, the groove width isrelatively large, though partially consumed by the chafer 28, and as ittraverses the side region, the width decreases and then widens outbefore decreasing again at the tread edge. The region of relativelygreater width in the central portion of the groove 38 is located atapproximately the mid-point of the side regions B. The portion of thegroove 38 with the greatest width, as measured perpendicular to thegroove centerline, has a maximum width Wx of 1.5 times the width Wn ofthe minimum groove width of the steeply slanted grooves 38.

As the tread edge, the inclination angle of the groove 38 increases,approaching 85°. At the tread edge, the grooves have an angle of70°–85°.

Circumferentially adjacent steeply slanted grooves 38 formcircumferentially adjacent rib blocks 40. The blocks 40 initiateadjacent to the rib 10 and extend to the tread edge. At the tread edge,the block width increases. The blocks 40 extend continuously through theside regions B, however, if desired for increased water flow andtraction, circumferential grooves may be provided in the side regions Bto form smaller blocks.

At the axially innermost edge 42 of the blocks 40, and extending intothe junction of adjacent steeply slanted grooves 38, are extendingsloping chamfers 44. Each chamfer 44 has a circumferential length of1/60^(th) to 1/40^(th) of the circumferential length of the tire.Relative to the circumferential length of the associated tread block 40,the chamfer 44 has a length of 5% to 20% of the block length, the blocklength being measured along parallel to the equatorial plane and excludethe chamfer length.

As the chamfer 44 extends into the junction of the grooves 38, the areaof the grooves decreases with increased height of the chamfer 44.However, due to the positioning of the block chamfer 44 adjacent to therib chamfers 38, the ability for water to flow into the grooves 38 isnot compromised. As the rib chamfer 28 decreases in width and height,the block chamfer 44 increases in width and height. The placement of thecircumferentially extending rib chamfers 28 in combination with thepredominately circumferentially extending block chamfers 44 effectivelyapproximate a pair of wide circumferential grooves. Thus, water flow inthe tread is maintained, as is the stiffness of the central treadregion.

The rib chamfer 44 can have any of the chamfer profiles as shown inFIGS. 2–5. When the chamfer of FIG. 5 is used as the rib chamfer 44, thechamfer edge that decreases in height should be the axially outer edge,relative to the EP. By placing this edge as the outer edge, water isdiverted into the grooves adjacent the rib 10.

The net-to-gross ratio of the tread, and the various regions of thetread, reflects the ability of the to move water. When viewed with justtwo zones, as illustrated in FIG. 1, the center region has anet-to-gross ratio of 50 to 63% and each side region has a net-to-grossratio of 55 to 70%.

To more fully appreciate the water flow capability of the tread,additional zones may be identified in each tread half. The zone Fencompassing the effectively created wide circumferential groovescreated by the adjacent chamfers, as measured from the axially innermostedge of the rib chamfer 28 and the axially outermost edge of the blockchamfer 44 has a net-to-gross ratio of 22 to 35% when the tread is new.As the tread wears, this net-to-gross ratio increases. From the axiallyoutermost edge of the block chamfer 44 to a location wherein the grooves38 begin to decrease in width, the zone C, has a net-to-gross ratio of50% to 65%. The axially outer edge of the tread, zone E, has anet-to-gross ratio of 75% to 85%, typically for the tread edges of atire to maintain tread edge stiffness. Extending from the tread edgetoward the tread center, the net-to-gross ratio decreases until itreaches a maximum at the tread center due to the rib 10.

Sipes 46 are spaced along the circumferential length of the block 40.The sipe density is the greatest toward the tread center and decreasesin the direction of the tread edges. At the axially inner portion of theblock 40, the sipe density has a maximum density of equal to the ribsipe density with a minimum density of 1 to 5 sipes per inch (0.393–1.97sipes/cm). At the axially outer portion of the block 40, the sipedensity is in the range of 0.5 to 3 sipes per inch (0.2 to 1.18sipes/cm). The variation in the block sipe density cooperates with thehigh density siping in the tread rib 10 to gradually vary the treadstiffness. Additionally, as noted previously, the heavier siping in thecenter of the tread improves the snow driving performance of the tire byincreasing the number of tread edges in the center of the tire whileproviding for a stiff tread at the outer tread zones.

At the axially outermost 25% of the each side region B, the sipes 46extend into the tread shoulders. To assist in water drainage andflexibility at the tread edge, the sipes 46 may have increased width, asillustrated at FIG. 1. Each sipe 46 in the shoulder has a wide widthportion 48 and a narrow width portion 50. In each block, the sipes 46are arranged so that the wide width portions 48 and the narrow widthportions 50 are circumferentially alternating.

For the directional tread illustrated in FIG. 1, the steeply slantedgrooves 38 in each side region B are mirror images, though laterallyoffset, of the steeply slanted grooves 38 in the opposing side region B.Also, due to the directional nature of the tread, all of the ribchamfers 28 are pointed in one direction and all the block chamfers 44are pointed in the opposing direction.

FIG. 7 illustrates the previously described tire tread as anon-directional tire tread. The steeply slanted grooves 38 in each sideregion B are laterally offset mirror inverse images of the grooves 38 inthe opposing side region B. The laterally oriented edges 24 of at thecenter one rib 10 are inclined in the same direction. To maintain theserrated configuration, the circumferentially extending edges 26 areinclined in the same direction, parallel to each other. The rib chamfers28 on opposing sides of the rib 10 point in opposing directions, whilethe block chamfers 44 in each side region B point in the oppositedirection from the block chamfers 44 in the opposing side region B.

The sipes 52 in the rib 10 of the non-direction tread are formed ofthree portions, wherein the first and third portions of the sipe 52 areinclined at substantially equal inclination angles. The block sipes inthe side regions B are inclined at angles substantially equal, but nomore than 10° greater, than the rib sipe portion located adjacent to therelative side region. In the instant tread, the overall sipe pattern forthe entire tread is inclined at an angle opposite that of the steeplyslanted grooves.

Other features of the non-direction tread may be identical to that ofthe directional tread, with permissible variations in accordance withthose already discussed.

1. A pneumatic tire comprising a tread and shoulders adjacent the tread,the tread comprising a central region and a pair of opposing sideregions, the tread further comprising a circumferentially extending ribin the central region, and a plurality of steeply slanted groovesinclined at an angle relative to the circumferential direction of thetire in each side region, the rib having a plurality of sipes extendingacross the full width of the rib, the sipes having a density of 2 to 8sipes per inch (0.78–3.15 sipes per cm), and the steeply slanted groovesin each side region initiate at the junction of the central region andthe side regions and terminate in the shoulders, formingcircumferentially adjacent tread blocks, the blocks extending from thecentral region to the shoulders, and having a plurality of sipes, thespacing between adjacent sipes increasing toward the tread shoulders,wherein the tread has a greater sipe density in the central region ofthe tire than in the side regions.
 2. The tire of claim 1 wherein thelateral edges of the rib have a plurality of laterally extending edgesand circumferentially extending edges, the laterally extending edges oneach side of the rib being circumferentially offset from the laterallyextending edges on the opposing side of the rib.
 3. The tire of claim 2wherein circumferentially extending from the laterally oriented edges ofthe rib, and along the lateral edge of the rib, is a chamfer thatdecreases in width from the laterally oriented edge to thecircumferentially adjacent laterally oriented edge.
 4. The tire of claim3 wherein the radial height of the rib chamfer gradually decreases fromthe laterally oriented edge to the circumferentially adjacent laterallyoriented edge.
 5. The tire of claim 3 wherein the sipes in the tread ribextend into the chamfer.
 6. The tire of claim 1 wherein the sipes in thetread rib are comprised of at least two inclined portions.
 7. The tireof claim 1 wherein the sipes in the blocks are oriented perpendicular tothe steeply slanted grooves.
 8. The tire of claim 1 wherein the sipes inthe tread rib have two sections formed of portions inclined at equal butopposing angles and the sipes in the blocks are inclined in the samedirection as the most adjacent sipe portion in the tread rib.
 9. Thetire of claim 1 wherein the steeply slanted grooves have a non-constantwidth as the grooves extend from the central region to the shoulders,the grooves having a maximum width in the central 15% of each sideregion of the tread.
 10. The tire of claim 9 wherein the grooves have amaximum width of at least 1.5 times the minimum groove width of thesteeply slanted grooves.
 11. The tire of claim 1 wherein the sipes inthe axially outermost 25% of each side region extend into the treadshoulders.
 12. The tire of claim 1 wherein at the axially inner portionof the block, the block has a sipe density of 1 to 5 sipes per inch(0.393–1.97 sipes/cm) and at the axially outer portion of the block, theblock has a sipe density of 0.5 to 3 sipes per inch (0.2 to 1.18sipes/cm).
 13. The tire of claim 1 wherein the net-to-gross ratio of thetire decreases from the tread edge toward the tread center, with amaximum net-to-gross ratio at the equatorial plane of the tire.
 14. Apneumatic tire comprising a tread and shoulders adjacent the tread, thetread comprising a central region and a pair of opposing side regions,the tread further comprising a circumferentially extending rib in thecentral region, and a plurality of steeply slanted grooves inclined atan angle relative to the circumferential direction of the tire in eachside region, the rib having a plurality of sipes extending across thefull width of the rib, the sipes having a density of 2 to 8 sipes perinch (0.78–3.15 sipes per cm), and the steeply slanted grooves in eachside region initiate at the junction of the central region and the sideregions and terminate in the shoulders, forming circumferentiallyadjacent tread blocks, the blocks extending from the central region tothe shoulders, and having a plurality of sipes, the spacing betweenadjacent sipes increasing toward the tread shoulders, and having sipesthat extending into the shoulder having a wide and a narrow widthportion, and the tread has a greater sipe density in the central regionof the tire than in the side regions.